Sharply directional wide band antenna



March 29, 1955 J. c. THQMAS 2,105,283

SHARPLY DIRECTIONAL WIDE BAND ANTENNA HTTOEA/EY March 29, 1955 J. c.THoMAs 2,705,283

sHARPLY DIREcTroNAL WIDE BAND ANTENNA Filed Feb. 12, 1954 5 Sheets-Sheet2 INVENTOR. JACK C. THOMAS March 29, 1955 J. c. THoMAs 2,705,283

SHARPLY DIRECTIONAL WIDE BAND ANTENNA Filed Feb. 12, 1954 5 Sheets-Sheet3 iig- 5.

IN VUV TOR. JACK c. //onAs March 29, 1955 J. c. THoMAs 2,705,283

SHARPLY DIRECTIONAL WIDE BAND ANTENNA Filed Feb. l2, 1954 5 Sheets-Sheet4 IN V EN TOR. dac /f C foM/L HTTOENEY March 29, 1955 J. c. THOMAS2,705,283

SHARPLY DIRECTIONAL WIDE BAND ANTENNA Filed Feb. l2, 1954 5 Sheets-Sheet5 53 'f: '1:1-l4 6 /NsuLnT/o/v 16 a9 Fia-l5 BY j/ AM HTTORNEY UnitedStates Patent C) SHARPLY DIRECTIONAL WIDE BAND ANTENNA Jack C. Thomas,Earlville, N. Y., assignor to Technical Appliance Corporation, Sherbume,N. Y., a corporation of New York Application February 12, 1954, SerialNo. 410,004

Claims. (Cl. Z50-33.51)

This invention relates to radio antennas, and more particularly itrelates to antennas which are specially designed for highly directionaleffects and with high gain over a wide radiation frequency band.

A principal object of the invention is to provide an improved antennafor use over two widely spaced frequency bands, such for example as inreceiving present day television frequencies both in the so-called lowfrequency band of television channels 2 to 6 (S4-88 megacycles), and inthe higher frequency band of television channels 7 to 13 (174-216megacycles).

With the advent of so-called compatible color television and with theadvent of increased radiation power of existing television transmitters,there has arisen a great need for a more sharply directional,mechanically sturdy and broad radiation frequency band antennastructure. Such an antenna must meet the following requirements.

1. Uniform coverage of low band frequencies in television channels 2-6,and high band frequencies in television channels 7-13, with higher gainon the latter channels.

2. High front-to-back ratio to eliminate co-channel interference orso-called "Venetion Blind effects encountered with increased transmitterpower.

3. Single forward lobe of all channels to meet the rigid requirements ofcolor television wherein ghosts show up as washed out tints or shades.

4. The antenna must be physically compact so that it may be readily usedwith conventional antenna rotators, even when the antenna consists of asingle coplanar array or of a multi-planar or stacked array.

5. The terminal impedance must match conventional 300 ohm transmissionlines for maximum transfer of signal to the receiver.

6. Multiple stacking must contribute corresponding added gain andcorresponding increased sharpening of the field intensity pattern.

In addition to the electrical requirements, the antenna must meet othertrade requirements as follows:

A. It must be easily assembled with a minimum of screws and nuts to betightened.

B. It should not be so bulky as to make handling during erectioncumbersome or dangerous to the installer.

C. It should be streamlined and sturdy to stand up in extreme weatherand icing conditions.

D. It must have a single boom and be collapsible to ft the smallestpackage, and also to facilitate stocking in jobbers, and dealers,premises and to permit transportation without danger of breakage.

The present invention has for one of its principal objects an antennawhich meets the above-noted requirements.

Another object is to provide a dipole antenna unit having each arm ofthe dipole sub-divided into one-half wavelength antenna sections bymeans of an intermediate phase converting unit which is also in the formof a radiation dipole.

Another object is to provide a dipole antenna comprised of a series ofco-linear one-half wavelength dipole elements with adjacent elementsrigidly and mechanically united in co-linear array and with the saidadjacent one-half wavelength elements electrically coupled by a phasecorrection radiation element.

A feature of the invention relates to a dipole antenna unit having eachdipole arm divided into a series of subice dipole sections which arerigidly united in co-linear array and with adjacent sectionselectrically interconnected by a folded dipole radiation element whichincreases the broad-banding effect while acting as a phase correctionelement at the higher frquencies. This phase correction elementmaintains the same current phase in all serially connected sub-dipolesections while maintaining substantially the same current distributionthroughout the various sub-dipole sections.

Another feature relates to an improved broad band antenna of the Yagitype having a series of one-half wavelength co-linear sub-dipolesections.

A further feature relates to a novel Yagi type antenna having at leasttwo driven units, a parasitic reflector unit, the driven units eachconsisting of a center one-half wavelength dipole section and at leastone additional one-half wavelength dipole section at opposite sides ofthe central section. The central section of each unit is coupled to theadjacent co-linear section by a respective folded dipole radiationelement whose longitudinal axis is substantially parallel to, but inspaced relation with, the associated interconnected sub-dipole sections.

A further feature relates to an antenna array of the one-half wavelengthdipole type employing at least two separate co-linear arrays, each arraybeing fed from the same transmission line, and each array consisting ofa series of serially spaced sub-dipole sections with adjacent sectionsinterconnected by respective folded dipole radiation elements.

A still further feature relates to the novel organization. arrangementand relative location and interconnection of parts which cooperate toprovide an improved directional and broad-band radiation antenna. Otherfeatures and advantages will be apparent after a consideration of thefollowing detailed description and the appended claims.

ln the drawing,

Fig. l is a top plan view of an antenna according to the invention;

Fig. 2 is a schematic diagram of one known type of antenna which isuseful in explaining the improvements of the present invention;

Fig. 3 is a schematic diagram similar to that of Fig. 2. butillustrating certain improvements in a simple colinear dipole accordingto the present invention;

Fig. 3A is a modification of the antenna of Fig. 3;

Fig. 4 shows graphs of the directional field pattern diagramscorresponding respectively to the antennas schematically shown in Figs.2 and 3;

Fig. 5 is an explanatory diagram of a conventional one-half wavelengthdipole antenna used in explaining the invention;

Fig. 6 is a graph of the directional field diagram of the antenna ofFig. 5;

Fig. 7 is an explanatory diagram of the conventional antenna of Fig. 5when operating at a higher frequency;

Fig. 8 is a graph of the directional eld diagram corresponding to theoperation of Fig. 7;

Figs. 9, l0, and l1 are respective sectional views of Fig. l, takenalong lines 9 9, 10-10, 11-11 thereof; F.Figi l2 is an enlarged view ofpart of the antenna of Fig. 13 is a sectional view of Fig. 12, takenalong the line 13-13 thereof;

Fig. l4 is an enlarged view of one of the swingable bracket supportsused in Fig. l;

Fig. 15 is a front view of Fig. 14;

Fig. 16 is a sectional view of Fig. l5, taken along the line 16-16thereof.

As is well known, a one-half wavelength dipole, as shown for example inFig. 5, provides the well-known pattern illustrated in Fig. 6 when itsphysical length is approximately one-half of the received wavelength. Asshown in Fig. 7, at a frequency where the overall physical length of theantenna is one and one-half times the received wavelength (for examplethe electrical length of a low band antenna operating in the higherfrequency band), the pattern changes to a clover leaf as shown in Fig.8. Here the one and one-half wavelength antenna action requires phasecorrection since the objectionable breaking up of the field pattern iscaused by the inner one-half wavelength element 10, 11 (Fig. 7),carrying currents inthe opposite direction to those in the outer onehalfwavelength elements 12, 13, as indicated by the dotdash curve. It isbecause of this current distribution that a low band dipole, which, forexample, may be designed to operate efficiently over television channels2 6, fails to give proper gain and pattern response in the higherfrequency band, for example channels 7-13. Various devices have beenproposed for correcting this condition. However, these prior proposals,while they have corrected the current distribution in the antennasections, have introduced other undesirable effects.

One proposed solution for this difficulty has been the division of eachphysical arm of the dipole into separate lengths which are electricallyconnected by lumped impedances either in the form of a resonant coil andcondenser combination, or in the form of so-called impedance stubs orquarter-wave transmission line sections. This latter form of the antennais illustrated in Fig. 2,

wherein the inner dipole sections 10, 1l. are connected they are ineffect high impedance one-quarter wave transi mission line sections.Consequently, at resonance, the current in the outer sections 12, 13, isnot equal to the current in the center section. This condition resultsin the limiting of the gain of the antenna at the higher frequencies.

I have found that this limitation can be overcome by interconnecting thecentral section with the respective outer sections by means of separateradiation elements such, for example, as folded dipole antenna elements.Such a structure is schematically illustrated in Fig. 3, wherein thecenter sections 10, 11, are connected to their respective outer sections12, 13, by the folded dipole antenna radiation elements 19, 20. I havefound that these elements 19 and 20 perform the triple function of,acting as phase conversion elements, as separate radiation elements, andthey also increase the broad-banding effect of the antenna. As a result,the current distribution in all the various sections of the antenna,represented by curves 21, 22, 23, are substantially uniform and theoverall current distribution has a smoothly curved characteristic 24, asdistinguished from the notched or non-uniform characteristic 26 of theantenna of Fig. 2.

These results are obtained by electrically connecting each folded dipoleelement 19 in series with the corresponding dipole arm sections. Forexample, folded dipole 19 is connected in series with arms 10 and 12;and folded dipole unit 20 is connected in series with arms l1 and 13.Each of the folded dipole units 19, 20, can be made of rigid wire or rodand with the longitudinal axis L extending parallel to the respectivesections 10 and 12 but preferably spaced a distance D therefrom. Sincethe folded dipole elements can be made of rod or wire of inherently lowimpedance they eliminate the blocking effect of one-quarter wave stubs,such as stubs 14 and 15 of Fig. 3, and increase the capture area of theantenna.

The folded dipole elements 19 and 20 act as phase reversing radiationelements whose impedance is constituted of resistance and reactance toprovide a much lower Q than a one-quarter wave line impedance stub whichhas only a reactive component. This combination, as illustrated in Fig.3, provides a broader effective band width to the antenna and increasesits effective frequency coverage while increasing its directionaleffects. There is shown in Fig. 4, by the dotted line curves 27, 28, thedirectional field intensity pattern of the antenna of Fig. 2, while thefull line curves 29, 30, represent the directional fiellil intensitypattern of the improved antenna illustrated in ig. 3.

While the invention has the above advantages when embodied in a simpleco-linear dipole antenna, as in Fig. 3, it also has important advantagesin connection with directionalized antennas of the generic Yagi type.Thus, as shown in Fig. 1, the main antenna or driven element isidentified by the numeral 31 which is the same as the antenna unit ofFig. 3, comprising a pair of aluminum or other conductive tubular rods32, 33, 34, 35, which are supported in spaced co-linear array. Thus,rods 32 and 33, at their inner ends are spaced apart and are suitablyanchored to an insulating block or strip 36 (see Fig. 10) which isanchored to the tubular metal cross piece 43. The rod 34 is supported inrigid alignment with rod 32 but insulated therefrom for example by aninsulator rod 37 which is tightly fitted at its opposite ends into thetubular members 32, 34. Metal sleeves 38, 39, can be staked on to themembers 32, 34 to firmly anchor the rod 37 in place. The rod 37 may bemade out of fiberglass or any other suitable insulator effective at highfrequency. Likewise, the rod 33 is anchored in rigid alignment with therod 35 by means of a similar insulator member 40 and the metal fasteningsleeves 41, 42.

The members 32, 34 and 37 are mounted for swinging movement as a unitwith respect to member 43, as likewise are the members 33, 35 and 40.For this purpose the insulation block 36 has pivotally attached theretoby respective pivot pins 44, (see Fig. 10) a pair of tubular metalmembers 46, 47, into which the inner ends of rods 32, 33 are fitted.Likewise pivotally attached to the block 36 are metal brackets 48, 49.The ends of these brackets are provided with off-set semi-cylindricalupper and lower tubular portions 50, 51, and 52, 53, to receive therespective antenna arms 32, 33. The undersurface of each of the bracketsis provided with a central rib 54, adapted to seat within acorresponding groove or channel in the upper face of block 36. A coiledspring 56 is located between the head 57 of pivot pin 54 and pressesagainst the bracket 48 to hold the parts 48, 36 and 46 in firm resilientengagement. Thus, when the arm 32 is swung to a position where it isperpendicular to member 43, rib 54 snaps into the recess in member 36 tolock the parts against relative swinging. A similar spring 58 isprovided for resiliently locking the parts 33, 47 and 49 in a positionperpendicular to member 43. In other words, the respective units (32,34, 37) and (33, 35, and 40) can be swung and detent locked in therelation shown in Fig. 1 when the antenna is being set up. For shippingor storage these units can easily be swung back to a positionsubstantially parallel to member 43 to conserve shipping or storagespace. This provides the necessary snap-locking action between the twolateral dipole units and the boom member 43 and does not require anyspecial tools or devices for making sure that the dipole arms are atright angles to the boom. Each of' the sleeves 38, 39 has a ange 59, 60(see Figs. 12 and 13) with a bore therethrough to receive the bent-backends 61, 62 of the folded dipole antenna element 63 which corresponds tothe element 19 of Fig. 3. Likewise there 1s supported in the flanges 64,65 of sleeves 41, 42, a similar dipole antenna element 66 whichcorresponds to element 20 of Fig. 3. Similarly, the members 32, 33 and34, 35, correspond respectively to elements 10, 11, 12 and 13 of Fig. 3.

The physical length of the two rods 32 and 33, taken together andallowing for the small gap between their adjacent ends, is approximatelyone-half wavelength to operate as a half-wave dipole in the upper end ofthe frequency band, e. g., television channels 7-13 (174-216megacycles). For example, if the antenna is designed to cover the range54 to 88 and 1.74 to 216 megacycles, the effective combined length ofrods 32 and 33 is approximately 31 inches. Likewise, each of thesections 34 and 35 has a physical length which is approximately equal tothat o f the combined rods 32, 33. Each of the small folded dipole units63 and 64 under the above conditions may have a length L ofapproximately l2 inches, a width W of approximately 2 inches, and aspacing S between the folded dipole and the associated rods 32 and 34 ofapproximately one and one-quarter inches with the gap G between the endsof the folded dipole approximately 1 inch. In any event under the abovefrequency assumptions each of the folded dipole units has its highestimpedance at approximately 225 megacycles which of course is above theupper frequency of the upper band. Each folded dipole element hassubstantial distributed reactance considered along the associatedantenna rods and is inductive over the entire frequency range of theantenna from 54 to 216 megacycles so that neither of the folded dipoleelements is resonant in this range.

Mounted in spaced relation to the main antenna driven unit 31 is anotherdriven unit 67 which is of substantially the same construction as themain driven unit 31 and is spaced from that driven unit a distance dapproximately equal to .34 wavelength at channel and .12 wavelength atchannel 4. Here again the unit 67 is formed with a central dipolesection consisting of the rods 68, 69, and the associated lateralsections 70, 71. The sections 68 and 70 are rigidly united and insulatedfrom each other in the same manner as the corresponding sections ofelement 31, and are connected in series by a folded dipole antenna unit72 which is designed substantially similar to the units 48 and 49 andthat unit 72 has its maximum impedance at approximately 225 megacycles,and is non-resonant in the frequency range between 54 and 216megacycles. A folded dipole unit 73, similar to unit 72, is connected inseries between the spaced ends of the rods 69 and 71. The elementsconstituting the driven unit 67 are supported on the boom 43 in the samemanner as described above in connection with antenna 31.

I have found that the best results are obtained where the unit 67,instead of being merely parasitically driven, as is the case in theconventional Yagi antenna, is also driven by being connected to the sametransmission line 74 which feeds the antenna 31 by means of metal straps75, 76. By this arrangement the cumulative energy in the antenna 31resulting from the direct pick up of the radiations and the parasiticradiations from the driven unit 67 is always combined in phaseregardless of the channel used.

In addition to the driven unit 67 there is provided a secondparasitically excited director 77 consisting of two one-half wavelengthmetal rods 78, 79, which are supported in rigid linear alignment andpivotally attached to the boom 43 in the same manner as described forantenna unit 31, and as shown in Fig. 1l. The parasitic director 77 isspaced from the driven unit 67 a distance d1 equal approximately to 0.18wavelength at channel 10 and .064 wavelength at channel 4. The director77 is split in the center by a one-quarter wave stub transmission line80 for maximum elciency in the high frequency band.

The stub 80 is designed so that it has its maximum impedance at afrequency of 325 megacycles well above the resonant frequency of thefolded dipoles 63, 66, 72, 73. Thus, if the folded dipoles are resonantat approximately 460 megacycles, which is well above the upper frequencyof 216 megacycles, then the stub 80 can have a minimum impedance atapproximately 700 megacycles. In other words, the resonant frequency ofeach of the folded dipoles is not less than twice the upper operatingfrequency of the antenna, and the resonant frequency of the stub 80 isnot less than three times the said upper operating frequency of theantenna.

The reector unit 81 for the higher end of the frequency band, forexample television channels 7-13, is made up of three rods 82, 83, 84,supported in rigid co-linear array but separated from each other by twoinsulator spacer rods 85, 86 in the same manner as for the rods 37-40.Here again, the unit is pivotally supported on the boom 43 in the samemanner as units 31, 67 and 77. The reflector 81 is spaced from theantenna unit 31 a distance d2 which is approximately .248 wavelength atchannel 10.

The reflector unit 87 for the lower end of the band, for exampletelevision channels 2-6, consists of two metal rods 88, 89 (see Fig. 9)and is spaced from the unit 31 a distance dZ-l-d3 which is approximately.175 wavelength at channel 4.

Since it is not necessary that the reflector unit 87 be insulated fromthe boom 43, it is not necessary to employ an insulating strip such asstrip 36. The arms 88 and 89 of reector 87 can be pivotally attached toboom 43 without intervening insulation. Therefore, instead of using aninsulator block 36, a metal block 90 can be rigidly fastened to the beam43, and the arms 88 and 89 can be swingably attached to this block in amanner similar to that described above in connection with the arms 32,33 and 78, 79.

In accordance with the well-known design principles of reflectors, thephysical length of each of the rods 82 83, 84, should be approximately1.09 times the length of the corresponding antenna rods 32-33, 34, 35.Likewise, the physical length of unit 87 should be approximately 1.06times one-half wavelength at channel 2. The director 78 should have aphysical length less than one-half wavelength at channel 13, andlikewise the director 79 should have a physical length less than onehalfwavelength at channel 10.

The antenna shown in Fig. 1 may be considered as made up of eleveneffective one-half wave sections, namely (32-33) 34, 35; (68-69), 70,71; 78, 79; 82, 83, 84; plus four phase reversing radiation elements 63,66, 72, 73. This provides a total of fifteen operating antenna elementsall of which contribute to the overall performance of the antenna in thehigher end of the television band. Considered from another viewpoint,the antenna arrangement consists of three Yagi systems. The iirst Yagisystem comprises elements (32-33), (68-69), 83; the second Yagi systemcomprises elements 34, 70, 82; the third Yagi system comprises theelements 35, 71, 84. The reflector 87, in addition to acting as areflector in the lower end of the band, for example television channels2-6, also acts as a shield which is effective in the higher end of theband to protect the system, when receiving the higher frequencies, frombeing substantially affected by radiation received from the oppositedirection. This increases the front-to-back ratio of the system.

It should be observed that the folded dipole elements 72, 73, 63, 66, donot act as phase reversing elements when the antenna is receivingsignals in the lower end of the band, because, in terms of wavelength atthose frequencies, the folded dipole units are too small in size to haveany phase reversing effect. However, they do have the important functionin the low bands of providing mutual coupling across the 2 inch gap,which results in a substantial increase in the fatness factor of theassociated elements and thus increasing the broad-banding efficiency ofthe antenna. Furthermore, since the folded dipole elements are connectedin series circuit with the respective antenna elements, these foldeddipole elements also help to raise the impedance of the antenna elementsto which they are connected and they effectively increase the elementlength. Since the folded dipole elements are of distributed reactance ascompared with lumped reactance and since they are not constituted ofsharply tuned condenser and inductor combinations, their impedance iseffective over the entire useful range of the antenna system.

While Fig. l shows a single bay antenna system, a vertically stackedseries of systems similar to those of Fig. l can be mounted insuperposed relation on the single vertical supporting mast, as iswell-known in the art.

While certain materials and dimensions have been referred to herein, itis done merely by way of illustration and not by way of limitation.Furthermore, while the driven antenna element 31 and the driven element67 are shown as being composed each of three one-half wave dipolesections connected by means of two intervening folded dipole units, agreater number of such sections and corresponding interconnected foldeddipole units may be employed. Furthermore, the Yagi can have more thanone drive or connected director. In other words, there may be three orfour elements like 31 and 67. rather than merely two, as shown in thedrawing. Furthermore, while the antenna has been described as primarilyuseful as a receiving antenna, it will be understood that it can also beused for transmission.

Various changes and modifications may be made in the disclosedembodiment without departing from the spirit and scope of the invention.For example, while for purposes of lightness in weight the antennaelements are preferably formed from hollow light-weight metal tubing, ifdesired the antenna units, including the folded dipole phase reversingelements, may be made out of respective single lengths of bendable rigidtubing. This arrangement is illustrated in Fig. 3A, wherein the foldeddipole element 19 and the folded dipole element 20 constitutes anintegral appropriately bent section at the appropriate point in thelength of each of the associated arms.

What is claimed is:

l. An antenna unit comprising at least three co-linear half-wave dipolesconsisting of a central dipole section and two lateral dipole sectionsarranged to operate efficiently over two widely spaced frequency bandsfor example 54-88 megacycles and 174-216 megacycles, means mechanicallyuniting all the sections as a co-linear array with the two lateralsections each having a respective insulated cap between it and theadjacent end of the center section, and separate folded dipole antennaelements each in the form of a flattened loop bridging a respective oneof said gaps and each forming an effective radiation element cooperatingwith the adjacent gapped sections which it bridges, each loop having anelectrical length which is approximately a half-wavelength and beingresonant at a frequency above the upper frequency range of the antennaunit and spaced from the gapped dipole sections which it bridges, whichspacing is a small fraction of the length of a dipole section, each ofsaid folded dipole elements having inherent resistance and capacitancecomponents to provide a broadbanding effect to the antenna unit and eachfolded dipole element being an effective radiation element for radiationin a direction normal to said co-linear array.

2. An antenna unit according to claim l in which each flattened loopdipole element has a major axis and a minor axis and the said spacingbetween the gapped co-linear dipole sections and the associated bridgingflattened loop dipole element is less than one-third the length of themajor axis of said element.

3. An antenna unit comprising at least three co-linear half-wave dipolesconsisting of a central section and two lateral sections arranged tooperate efficiently over two widely spaced frequency bands for example54-88 megacycles and 174-216 megacycles, means mechanically uniting allthe sections in a co-linear array unit with the two lateral sectionseach having a respective insulated gap between it and the adjacent endof the center section, and separate folded dipole antenna elements eachin the form of a flattened loop bridging a respective one of said gapsand each forming an effective radiation element cooperating with thegapped sections which it bridges to bring the currents in said sectionsinto like phase at the higher one of said frequency bands, each foldeddipole element having a major axis substantially parallel to saidco-linear array which major axis has a length which is approximately 0.2wavelength at a chosen frequency within said higher band, and having aminor axis which is approximately 0.033 wavelength at said chosenfrequency, the side of folded dipole element adjacent said co-linearsections being spaced therefrom a distance of approximately 0.02wavelength at said chosen frequency, each folded dipole element being aneffective radiation element over both said bands for radiation mainly ina direction normal to said co-linear array.

4. An antenna unit according to claim 3 in which each of said gaps isapproximately 0.018 wavelength at said chosen frequency.

5. An antenna unit according to claim 1 in which adjacent gappedco-linear sections are located in the same plane as the folded dipoleelement which bridges the gap therebetween to provide substantial mutualcoupling and energy transfer between the said sections which said foldeddipole element bridges.

6. An antenna unit according to claim 5 in which each of said foldeddipole elements forms a phase inverter for frequencies in the upper oneof said bands while providing mutual coupling between its bridgedco-linear sections in the lower one of said bands.

7. An antenna system including at least two similar antenna units eachunit comprising at least three co-linear half-wave dipoles consisting ofa central dipole section and two lateral dipole sections arranged tooperate eiciently over two widely spaced frequency bands for example54-88 megacycles and 174-216 megacycles, means mechanically uniting allthe sections as a co-linear array with the two lateral sections eachhaving a respective insulated gap between it and the adjacent end of thecenter section, and separate folded dipole antenna elements each in theform of a flattened loop bridging a respective one of said gaps and eachforming an effective radiation element cooperating with the adjacentgapped sections which it bridges, each loop having an electrical lengthwhich is approximately a half-wavelength and being resonant at afrequency above the upper frequency range of the antenna unit and spacedfrom the gapped co-linear dipole sections which it bridges, whichspacing is a small fraction of the length of a dipole section, each ofsaid folded dipole elements having inherent resistance and capacitancecomponents to provide a broad-banding effect to the antenna unit andeach folded dipole element being an effective radiation element forradiation in a direction normal to said co-linear array, means tosupport both said antenna units in substantial parallelism, and meansfor connecting the central sections of each unit to a transmission line.

8. An antenna system according to claim 7 in which there is provided forthe higher frequency band a first parasitic reflector array which ismounted in spaced parallelism with both of said units, said parasiticarray comprising a central section in alignment with the central dipolesections of each of said antenna units, said parasitic array alsoincluding lateral sections each in alignment with the correspondinglateral sections of both of said antenna units, the central section andlateral sections of said parasitic array being co-linear and insulatedfrom each other.

9. An antenna system according to claim 8 in which there is provided forthe lower frequency band a separate parasitic reflector array which ismounted in spaced parallelism with the first parasitic array.

10. An antenna system according to claim 9 in which a parasitic directorarray is mounted in spaced parallelism with said antenna units, saidparasitic director array comprising a pair of co-linear elements with aninsulated gap between the adjacent ends thereof and a quarter-wave stubtransmission line bridging said gap between said colinear parasiticdirector elements, said stub line having a resonant frequency well abovethe upper operating frequency of the antenna system.

References Cited in the file of this patent UNITED STATES PATENTS1,957,949 Franklin et al. May 8, 1934 1,967,881 Green July 24, 19342,130,387 Franklin Sept. 20, 1938 2,248,800 Alford July 8, 19412,380,333 Scheldorf July 10, 1945 2,655,599 Finneburgh, Jr. Oct. 13,1953 2,688,083 Hills Aug. 31, 1954

